In vehicles having internal combustion engines, it can be beneficial to discontinue Fuel injection to all or some of the engine cylinders during certain operating conditions, such as during vehicle deceleration or braking. The greater the number of cylinders deactivated, or the longer cylinders are deactivated, the greater the fuel economy improvement that can be achieved.
However, the inventors herein have recognized that poor drivability may become an issue during deceleration fuel shut off (DFSO). For example, a potential exists for poor drivability when the vehicle operator releases and subsequently engages the accelerator pedal. Specifically, as described in U.S. Pat. No. 6,266,597, poor drivability may result due to transmission or driveline gear lash. In particular, when the engine transitions from exerting a positive torque to exerting a negative torque (or being driven), the gears in the transmission or driveline separate at the zero torque transition point. Then, after passing through the zero torque point, the gears again make contact to transfer torque. This series of events produces an impact, or clunk.
Further, the inventors have also recognized that it can take a certain duration (e.g., amount of time, or number of engine cycles) to re-enable engine firing. Thus, when exiting DFSO (e.g., re-enabling injectors), a driver may feel clunk if the injectors, combustion, transmission control and engine torque control do not have adequate time to stabilize. Alternatively, if additional time is taken to re-enable engine operation to reduce clunk, the driver may experience a delayed vehicle response, thus potentially causing the vehicle to feel sluggish.
In one embodiment, at least some of the above issues may addressed by a method of controlling fuel injection in an engine of a vehicle comprising reactivating fuel injectors based on release or decrease of driver braking during deceleration fuel shut off.
In this way, the engine can exit DFSO (e.g., re-enable combustion) earlier by making use the brake input and effort, which allows time to reactivate the fuel injection and stabilize torque control prior to a tip-in. Thus, noise, vibration, and harness may be improved by preparing torque control for a tip-in prior to the event.
According to another aspect, a method of controlling fuel injection in an engine of a vehicle comprises reactivating fuel injectors based on release or decrease of driver braking during deceleration fuel shut off; and increasing air flow to a cylinder before reactivation of fuel injectors in response to said release or decrease of driver braking to enhance torque response.
Such operation can provide several advantages. For example, increasing air flow to cylinders can reduce a potential for engine misfire and provide faster torque response. According to yet another aspect, a vehicle control method is provided for a vehicle having an internal combustion engine coupled to a torque converter. The torque converter also includes a speed ratio from torque converter output speed to torque converter input speed, and the torque converter is coupled to a transmission. The method comprises reactivating fuel injectors based on release or decrease of driver braking during deceleration fuel shut off during a first condition where the engine speed is less than a predetermined speed; and maintaining deactivation of fuel injector during a release or decrease of driver braking during deceleration fuel shut off during a second condition where the engine speed is greater than said predetermined speed.
Again, the approach has various advantages. For example, since a driver may feel clunk to a greater degree as engine speed decreases, the above approach reactivates fuel injection during such conditions to improve a driver's feel; but maintain DFSO under other conditions to improve fuel economy where driver's feel is affected to a lesser degree.